Sequential ion, UV, and electron induced chemical vapor deposition

ABSTRACT

Ion-induced, UV-induced, and electron-induced sequential chemical vapor deposition (CVD) processes are disclosed where an ion flux, a flux of ultra-violet radiation, or an electron flux, respectively, is used to induce the chemical reaction in the process. The process for depositing a thin film on a substrate includes introducing a flow of a first reactant gas in vapor phase into a process chamber where the gas forms an adsorbed saturated layer on the substrate and exposing the substrate to a flux of ions, a flux of ultra-violet radiation, or a flux of electrons for inducing a chemical reaction of the adsorbed layer of the first reactant gas to form the thin film. A second reactant gas can be used to form a compound thin film. The ion-induced, UV-induced, and electron-induced sequential CVD process of the present invention can be repeated to form a thin film of the desired thickness.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the chemical vapor deposition processes used inthe fabrication of semiconductor devices, and more particularly tomethods for sequential chemical vapor deposition of thin films.

2. Description of the Related Art

Chemical vapor deposition (CVD) is one of the principal methods used insemiconductor fabrication to form a variety of thin films, includingdielectric and conductive layers. In chemical vapor deposition, amaterial layer is formed by the reaction of gas phase reactants at ornear a substrate surface. Various methods of energy input can be used topromote the chemical reaction, including thermal energy, photons, andplasma. In a plasma-assisted CVD process, the reaction is promoted byactivating the gas phase reactants to form radical species, electronsand ions, which form a plasma. Background gases which participate informing a plasma, but may or may not participate in the depositionreaction may also be included in plasma-assisted CVD processes. Theproperties of the deposited material, as well as the rate at whichmaterial is deposited may depend on precursor gases to the gas phasereactants, on the background gases, and on the plasma conditions.

Advances in semiconductor devices increase the demands for chemicalvapor deposition of highly conformal and uniform thin films. Inconventional CVD processes, it is often difficult to obtain a thin filmthat is conformal across the entire surface of a wafer, particularlywhen the wafer has a large radius. Furthermore, in conventional CVDprocesses, reaction byproducts often get trapped in the film beinggrown, affecting the purity and the electrical properties of the film.

U.S. Pat. No. 4,058,430 of Suntola et al. describes an atomic layerepitaxy (ALE) process for growing compound thin films. In the ALEprocess of the '430 patent, a substrate is exposed to the vapor of afirst element in a reaction chamber and the substrate is heated to atemperature sufficiently high to induce a chemical reaction between thefirst element and the substrate for forming a single atomic layer of thefirst element on the substrate surface. The heated substrate can besubsequently exposed to the vapor of a second element to form a singleatomic layer of the second element on top of the atomic layer of thefirst element. The process is repeated until the compound film reaches adesired thickness. U.S. Pat. No. 4,398,973 also of Suntola et al.describes an alternate method of performing the ALE process to the '430patent which uses gaseous compounds to supply the reactive elements.These techniques for ALE processes relate more closely to CVD processes.

In both the '430 and '973 patents, the ALE process is driven by thermalenergy through heating the substrate. Specifically, the temperature ofthe substrate has to be high enough to prevent condensation of theelements on the surface of the substrate and to induce chemical reactionbetween the reactive elements and the substrate surface. A disadvantageof the ALE process of the '430 and '973 patents is that when formingcompound thin films, the different reactive elements must haveoverlapping temperature windows for forming a saturated layer in orderto perform the ALE process. Thus, the ALE process of the '430 and '973patents has limited applications.

U.S. Pat. No. 5,916,365 describes a sequential chemical vapor depositionprocess where a first reactant forms a saturated layer on the surface ofa substrate and a second reactant is passed through a radical generatorwhich activates the second reactant into a gaseous radical. The gaseousradical of the second reactant is used to induce a chemical reaction ofthe saturated layer. An disadvantage of the process disclosed in the'365 patent is that the reactive species in the CVD process are limitedto free radical species that are generated by the radical generator.Radical generators that can be used in the '365 process generally useplasma discharges to break up most of the bonds in the precursor gas.Thus, the radical generation process is non-selective and all types ofradicals, whether beneficial or harmful to the deposition process ofinterest, are generated. Furthermore, radical generators also sufferfrom contamination problems as some gases tend to cause a film to bedeposited on the walls of the generators.

It is desirable to provide a sequential chemical vapor depositionprocess with improved process characteristics and also capable offorming a variety of compound thin films with improved film properties.

SUMMARY OF THE INVENTION

According to the present invention, ion-induced, UV-induced, andelectron-induced sequential chemical vapor deposition (CVD) processesare disclosed where an ion flux, a flux of ultra-violet radiation, or anelectron flux, respectively, is used to induce a chemical reaction forforming a thin film. In one embodiment, a process for depositing a thinfilm on a substrate includes the steps of: (a) placing the substrateinto a process chamber; (b) evacuating the process chamber; (c)introducing a flow of a first reactant gas in vapor phase into theprocess chamber where the first reactant gas forms an adsorbed saturatedlayer on the substrate; (d) evacuating the process chamber; (e) exposingthe substrate to a flux of ions for inducing a chemical reaction of theadsorbed saturated layer of the first reactant gas to form the thinfilm; and (f) evacuating the process chamber. In other embodiments,instead of using a flux of ions, a flux of UV light or a flux ofelectrons is used to induce the chemical reaction.

When a compound thin film is desired, the process of the presentinvention can include: (g) before exposing the substrate to a flux ofions, introducing a flow of a second reactant gas in vapor phase intothe process chamber. The flux of ions induces a chemical reaction of theadsorbed saturated layer of the first reactant gas and the secondreactant gas for forming a compound thin film. Again, in otherembodiments, instead of using a flux of ions, a flux of UV light or aflux of electrons is used to induce the chemical reaction.Alternatively, the process for forming a compound thin film can include:(g) introducing a flow of a second reactant gas in vapor phase into theprocess chamber; (h) exposing the substrate to a flux of ions forinducing a chemical reaction of the adsorbed saturated layer of thefirst reactant gas and the second reactant gas to form a compound thinfilm; and (i) evacuating the process chamber.

The present invention is better understood upon consideration of thedetailed description below and the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, a sequential chemical vapordeposition (CVD) process uses either an ion flux, a flux of ultra-violetradiation, or an electron flux as energy input for driving the chemicalreaction to form a thin film. The ion-induced, UV-induced, orelectron-induced sequential CVD process of the present inventiondeposits a saturated layer of an element or a compound at a time. Theprocess can be repeated to form a thin film of any desired thickness. Athin film formed using the sequential CVD process of the presentinvention is uniform and highly conformal. Furthermore, the sequentialCVD process of the present invention can be used to form elemental orcompound thin films of a wide range of reactive elements since theprocess can be carried out in a broad temperature window. These andother advantages of the ion-induced, UV-induced, or electron-inducedsequential CVD process of the present invention will become moreapparent in the description below.

The ion-induced, UV-induced, or electron-induced sequential CVD processof the present invention is carried out in a process chamber, such as aCVD reactor. Suitable process chambers include any conventionallow-pressure CVD (LPCVD) reactors or any conventional plasma CVDreactors. As is well known in the art, there are two main types ofplasma CVD reactors, hence two main plasma CVD processes. When acapacitively coupled parallel plate reactor is used, the depositionprocess is conventionally termed plasma-enhanced CVD (PECVD). The plasmamay be formed in the PECVD reactor by a radio frequency (rf) dischargeat a single frequency. An example of a PECVD reactor is the Sequel™reactor of Novellus Systems (San Jose, Calif.). Alternatively, a highdensity plasma reactor (HDP) in which the plasma is formed by electroncyclotron resonance (ECR) or as an inductively coupled plasma (ICP) maybe used. An optional rf bias of a different frequency may be applied inHDP reactors. An example of an HDP reactor is the Speed™ reactor ofNovellus Systems.

While in the present description, the process chamber is a CVD reactor,one of ordinary skill in the art would appreciate that any type ofprocess chamber can be used to practice the processes of the presentinvention. For example, the present invention can be carried out in aphysical vapor deposition (PVD) chamber or other commonly availablesemiconductor processing chamber, with appropriate modifications. Infact, a process chamber suitable to practice the processes of thepresent invention can be any enclosure equipped with one or more gasinlets, at least one gas outlet for evacuating the enclosure, and asource for providing the energy input for driving the chemical reactionin the process, as will be described in more detail below.

The ion-induced, UV-induced, or electron-induced sequential CVD processof the present invention can be used to deposit elemental or compoundthin films on the surface of a substrate. Examples of thin films whichcan be formed using the process of the present invention includedielectric layers, such as silicon dioxide or aluminum oxide layers, andconductive layers, such as titanium or titanium nitride layers. Thesubstrate is typically a semiconductor substrate, such as a siliconwafer, commonly used in the fabrication of integrated circuit devices.Of course, other types of substrates can also be used.

According to the ion-induced, UV-induced, or electron-induced sequentialCVD process of the present invention, a substrate is introduced into aCVD reactor. Typically, the reaction chamber of a CVD reactor can holdone or more substrates. However, for simplicity of discussion, it isassumed that only a single substrate is introduced into the CVD reactor.The CVD reactor is evacuated as needed by a suitable pump. In thepresent embodiment, the CVD reactor is operated at low pressure. Ingeneral, the total pressure in the reactor can be maintained at lessthan about 10 torr. In other embodiments, the CVD reactor can beoperated at a pressure ranging from atmospheric pressure to lowpressure.

The substrate is heated to a desired temperature such as by placing thesubstrate on a suitable platform including a heating element. Othermethods for heating the substrate can also be used, such as using RFinduction heating or using photons. The substrate is typically heated toa temperature of about 50° C. to 400° C., depending on the types of thinfilms being deposited. The temperature of the substrate is selected tobe sufficiently high to prevent condensation of the reaction gases onthe surface but allow adsorption, or more particularly chemisorption, totake place for forming a saturated layer of the reactive elements to beintroduced.

Next, a flow of a first reactant gas is introduced into the CVD reactor.The reactant gas is introduced in vapor phase as is conventionally donein CVD processes. The first reactant gas is adsorbed on the surface ofthe substrate and forms a saturated layer of the reactant element. Thetime required to form a saturated layer of the first reactant is short,typically in the range of 1-30 seconds. Then, the CVD reactor isevacuated of excess reactant.

According to a first embodiment of the present invention where anion-induced sequential CVD process is used, the substrate surface withthe saturated layer of the first reactant element is exposed to a fluxof ions. The ions induce a chemical reaction either in the adsorbedsaturated layer or between the saturated layer and the substrate surfacefor forming a thin film of approximately one saturated layer. Thereaction time depends on the reactive species. The CVD reactor can thenbe evacuated of excess gases and reaction by-products. The processsequence can be repeated by introducing a flow of the first reactant gasagain. The process is repeated until a thin film of the desiredthickness is deposited.

When only one reactant gas is used in the ion-induced sequential CVDprocess of the present invention, an elemental thin film is formed onthe surface of the substrate. For example, in a process to deposit atitanium thin film on a substrate, titanium tetrachloride (TiCl₄) isused as the reactant gas and is introduced into a CVD reactor where theTiCl₄ molecules are adsorbed on the substrate surface forming asaturated layer. Then, the reaction chamber is evacuated and a flux ofions is introduced into the CVD reactor. The ion flux induces a chemicalreaction in the TiCl₄ saturated layer such that chlorine atoms aredislodged from the TiCl₄ molecules and a saturated layer of titanium isformed.

The ion-induced sequential CVD process of the present invention can alsobe used to form compound thin films. To form a compound thin film, asecond reactant gas containing the necessary reactive species is used.In another embodiment of the ion-induced sequential CVD process of thepresent invention, a flow of the second reactant gas is introduced intothe CVD reactor after the first reactant gas forms a saturated layer andthe reactor is evacuated. The second reactant gas does not necessarilyform a saturated layer on the surface but instead is available to reactwith the saturated layer of the first reactant. While the flow of thesecond reactant gas is being introduced into the CVD reactor, thesubstrate is exposed to a flux of ions which induces a chemical reactionbetween the first reactant in the saturated layer and the secondreactant gas for forming a compound thin film. The CVD reactor isevacuated of excess gases and reaction byproducts after the chemicalreaction is completed and a film of approximately one saturated layer isthus formed. The process sequence can be repeated by introducing thefirst reactant gas into the CVD reactor again to form a saturated layer.The process sequence can be repeated multiple times to form a thin filmof desired thickness. In other embodiments, the flow of the secondreactant gas can be introduced and evacuated before the substrate isexposed to a flux of ions.

In another embodiment of the ion-induced sequential CVD process, thesecond reactant gas is introduced after the saturated layer of the firstreactant gas has been exposed to a flux of ions. In this embodiment,after the first reactant forms a saturated layer and the chamber isevacuated, the saturated layer is then exposed to a flux of ions whichinduces a chemical reaction in the saturated layer as described abovefor forming a thin film of approximately one monolayer thick.Subsequently, the chamber is evacuated again and a flow of the secondreactant gas is introduced into the reactor. During, or after, thesecond reactant gas is introduced into the reactor, the CVD reactor isagain subjected to a flux of ions which induces a chemical reactionbetween the thin film on the substrate surface and the second reactantgas. Consequently, a compound thin film is formed containing elements ofthe first reactant gas and the second reactant gas. After the reactionis completed, the CVD reactor is evacuated of excess gases and othervolatile reaction byproducts generated during the chemical reaction. Theprocess sequence can be repeated by introducing the first reactant gasinto the reactor again for forming a saturated layer. The processsequence can be repeated to form a compound thin film of the desiredthickness.

The ion flux used to induce the chemical reaction in the sequential CVDprocess of the present invention can be inert gas ions, such as argon,or reactive gas ions, such as nitrogen, oxygen, or hydrogen. Typically,inert gas ions or hydrogen ions are used when forming elemental thinfilms. For instance, argon ions can be used to induce a chemicalreaction of an adsorbed saturated layer of TiCl4 molecules to form anelemental titanium thin film. On the other hand, reactive gas ions canbe used instead to provide the necessary reactive species. The reactivegas ions can be multiatomic ions containing the necessary reactivespecies. For example, when titanium nitride thin film is to be formed, afirst reactant gas of titanium tetrachloride can be used to form asaturated layer of titanium tetrachloride. Then the saturated layer canbe exposed to a flux of reactive nitrogen ions from an N₂ or an NH₃ gas.The reactive nitrogen ions induce a chemical reaction in which chlorineatoms are separated from the titanium tetrachloride molecules andnitrogen atoms are bound to the titanium, forming a titanium nitridelayer. The process is repeated to form a titanium nitride film of thedesired thickness.

The ion flux used in the sequential CVD process of the present inventioncan be generated in a number of ways. As is well known in the art, onemethod for generating ions is impact ionization where a gas source isionized by electrons. The electrons can be generated by a hot filamentor other means known in the art. Other methods for generating ionsinclude discharge processes such as a DC plasma discharge or a RF plasmadischarge.

When a plasma discharge process is used as an ion source, a gas sourceis introduced into the CVD reactor and plasma energy is supplied to thereactor either through DC or RF coupling. The plasma energy ionizes theintroduced gas and generates the necessary ions for the sequential CVDprocess. The ion source can be physically separated from the main CVDreactor chamber or the ion source can be a part of the reactor chamber.If the ion source is not in close proximity to the reaction chamber, aseries of electrostatic or magnetic elements will be required to directthe ions to the substrate. If the ion source is close to the reactionchamber, a simple drift tube will suffice to direct the ions to thesubstrate. Also, the ion source can be spaced apart from the substratesurface or it can be in close proximity to the substrate surface. As iswell known in the art, the ion energy of the ions can be controlledeither by controlling the energy of the ions itself or by biasing thesubstrate accordingly.

According to another embodiment of the present invention, in anUV-induced sequential CVD process, a flux of ultraviolet (UV) lightprovides the energy input for driving the chemical reaction in theprocess, instead of the flux of ions in the ion-induced process. Thus,according to the present embodiment, a substrate is introduced into aCVD reactor. In the present embodiment, the CVD reactor is operated atlow pressure. The CVD reactor is evacuated to remove excess gases. Aflow of a first reactant gas is introduced into the reactor and forms asaturated layer on the surface of the substrate by adsorption. Then thereactor is evacuated of excess gases. The substrate can then be exposedto a flux of UV light to induce a chemical reaction in the saturatedlayer to form a thin film. The reactor is then evacuated of excess gasesand reaction byproduct.

As in the case of the ion-induced sequential CVD process, the UV-inducedsequential CVD process can be used to form compound thin films. Thus, inanother embodiment, after the saturated layer of the first reactant isexposed to UV light and the reaction chamber is evacuated, a flow of asecond reactant gas is introduced into the reactor. During, or after,the second reactant gas is being introduced, the substrate is exposed toa flux of UV light to induce a chemical reaction between the firstreactant in the saturated layer and the second reactant. Alternatively,before exposing the saturated layer of the first reactant to the UVlight, a flow of a second reactant gas is introduced into the CVDreactor and the UV light induces a chemical reaction between thesaturated layer of the first reactant and the second reactant. Afterforming a thin film of approximately one saturated layer, the CVDreactor is evacuated of excess gas and reaction byproducts. Of course,the process can be repeated to form a compound thin film of the desiredthickness.

In the UV-induced sequential CVD process of the present invention, theUV radiation must be of a high enough energy to induce the chemicalreaction of the reactive species of interest. The UV light can begenerated from a broad band source such as a black body source. Whenblack body radiation is used to generate the UV light, the source is runat a sufficiently high temperature to generate a high enough flux of UVradiation at a wavelength short enough to induce the chemical reaction.The UV light can also be generated from a variety of plasma discharges.For example, a mercury discharge lamp generates a large amount of UVradiation. A DC or RF plasma discharge can also be used. When RFdischarge is used, the electrodes can either be located inside thedischarge region or they can be located external to the dischargeregion. The RF energy can be capacitively or inductively coupled orboth. A variety of lasers can also be used to supply the required fluxof UV radiation. The UV source can be separate from the CVD reactor orbe a part of the reactor. The UV source can be spaced apart from thesubstrate or it can be in close proximity to the substrate.

According to another embodiment of the present invention where anelectron-induced sequential CVD process is used, a flux of electrons isused as the means for inducing the chemical reactions in the CVDprocess, as opposed to a flux of ions or a flux of UV light, asdescribed above. Thus, according to the present embodiment, a substrateis introduced into a CVD reactor. In the present embodiment, the CVDreactor is operated at low pressure. The CVD reactor is evacuated toremove excess gases. A flow of a first reactant gas is introduced intothe reactor and forms a saturated layer on the surface of the substrateby adsorption. Then the reactor is evacuated of excess gases. Thesubstrate can then be exposed to a flux of electrons to induce achemical reaction in the saturated layer. The reactor is then evacuatedof excess gases and reaction byproduct.

The electron-induced sequential CVD process can also be used to formcompound thin films as in the case of the ion-induced and UV-inducedsequential CVD processes. Thus, in another embodiment, after thesaturated layer of the first reactant is exposed to an electron flux andthe reaction chamber is evacuated, a flow of a second reactant gas isintroduced into the reactor. During, or after, the second reactant gasis being introduced, the substrate is exposed to a flux of electrons toinduce a chemical reaction between the first reactant and the secondreactant. Alternatively, before exposing the saturated layer of thefirst reactant to the electron flux, a flow of a second reactant gas isintroduced into the CVD reactor and then the substrate is exposed to theflux of electrons which induces a chemical reaction between thesaturated layer of the first reactant and the second reactant. Afterforming a thin film of approximately one saturated layer, the CVDreactor is evacuated of excess gas and reaction byproduct. Of course,the process can be repeated to form a compound thin film of the desiredthickness.

In the electron-induced sequential CVD process, the electron flux can begenerated from a hot filament as is conventionally done. The electronscan also be generated photoelectrically, such as by exposing an emittingsurface to light of sufficient energy to induce the photoelectriceffect. The electrons can also be generated from a variety ofdischarges, such as a DC plasma discharge or a RF discharge. Theelectron source can be separate from the CVD reactor or be a part of thereactor. The electron source can be spaced apart from the substrate orit can be in close proximity to the substrate.

The ion-induced, UV-induced and electron-induced sequential CVD processof the present invention is capable of depositing thin films withimproved film properties. Because the thin film is deposited as onesaturated layer at a time, excellent uniformity and conformal stepcoverage can be achieved. Furthermore, the uniformity of the film can betailored since the film is deposited as one saturated layer at a time.Thus, the concentration of one element of a film can be gradually orabruptly altered throughout the thickness of the thin film as desired.For example, a titanium-titanium nitride thin film can be depositedwhere the bulk of the film is elemental titanium and the near-surfacelayers of the film are titanium nitride.

By using an ion flux, an UV flux, or an electron flux to drive thereaction, the ion-induced, UV-induced and electron-induced sequentialCVD process of the present invention can be operated at a lowertemperature range than the prior art processes. Furthermore, becauseonly one saturated layer is needed to form the thin film, the processcan be used to form compounds of a variety of materials. Moreover, theadsorption process to form a saturated layer is relatively independentof gas flow rate, rendering the process more tolerant of manufacturingconditions. Because the thin film of the present process is formed froma saturated layer, the spatial uniformity of the ion, UV or electronflux impinging on the surface is not critical to the process. Thesequential CVD process can be carried out as long as a sufficientquantity of ions, UV photons or electrons are provided to the substrateto complete the reaction. Thus, the ion-induced, UV-induced andelectron-induced sequential CVD process of the present invention has awide process tolerance and improved manufacturability. Other advantagesof using ions, electrons and UV photons/radiation include the ability toadjust various process parameters in the sequential CVD process so as toproduce the desired thin film. For instance, adjusting the flux and theincident energy of the ions, electrons or UV photons may be useful inselecting the desired chemical reaction in the CVD process for forming aspecific film of interest. In the ion-induced and electron-inducedsequential CVD processes, the voltage of the ions and electrons can beadjusted electrostatically. On the other hand, in the UV-inducedsequential CVD process, the wavelength of the UV photons can beadjusted. For example, the wavelength of a laser can be varied and thewavelength of a continuous source can be filtered to give the desiredwavelength. Furthermore, a variety of lamp sources that emit differentwavelengths can also be used.

The following examples are provided to illustrate the application of theion-induced, UV-induced, or electron-induced sequential CVD process ofthe present invention in the formation of a titanium film and a titaniumnitride film. The process conditions are illustrative only and a personof ordinary skill in the art would know how to modify the processconditions to obtain the desired process characteristics and filmproperties.

To form a layer of titanium on a silicon substrate, a first reactant gasof titanium tetrachloride (TiCl₄) is used. When the substrate is exposedto the TiCl₄ gas, the TiCl₄ gas molecules are adsorbed onto the surfaceof the substrate and a saturated layer of TiCl₄ is formed. Then thesubstrate is exposed to a flux of hydrogen ions (H⁺) which reacts withthe chlorine atoms in the saturated layer, forming hydrogen chloride.Hydrogen chloride is a volatile reaction byproduct and is exhausted outof the CVD reactor. When the reaction is complete, a saturated layer oftitanium atoms is left on the silicon substrate. Alternatively, insteadof hydrogen ions, a flow of hydrogen (H₂) gas can be used in thepresence of a UV light source. The UV light functions to break the bondsof the H₂ molecules, making the hydrogen atoms available to react withthe chlorine atoms in the saturated layer. The UV light also functionsto break the bonds between the chlorine atoms and the titanium atoms,allowing the chlorine to react freely with the hydrogen. In yet anotherembodiment, instead of hydrogen ions, a flow of hydrogen (H₂) gas can beused in the presence of a flux of electrons. The electrons function todissociate the bonds between the H₂ molecules and between the chlorineand titanium molecules. Hydrogen and chlorine react, forming a volatilereaction byproduct. A titanium saturated layer results.

To form a layer of titanium nitride, titanium tetrachloride (TiCl₄) andammonia (NH₃) are used. When the ion-induced sequential CVD process isused, a substrate with a saturated layer of TiCl₄ is exposed to a flowof NH₃ gas. While the flow of NH₃ gas is being introduced, the substrateis subjected to a flux of ions which dissociates the bonds between thenitrogen and hydrogen atoms of the NH₃ gas and the chlorine and titaniumatoms of the TiCl₄ gas. The nitrogen atoms react with the titaniumatoms, forming a saturated layer of titanium nitride. Alternatively,when the UV-induced sequential CVD process is used, the substrate with asaturated layer of TiCl₄ can be first subjected to a flux of UV lightwhich functions to dissociate the chlorine atoms from the titaniumatoms. Then, a flow of NH₃ gas is introduced which reacts with thetitanium to form titanium nitride. By using this process sequence, it ispossible to avoid exposing the second reactant gas to UV light which maybe desirable in some situations.

The above detailed descriptions are provided to illustrate specificembodiments of the present invention and are not intended to belimiting. Numerous modifications and variations within the scope of thepresent invention are possible. For example, in the above embodiments,the process chamber is described as being operated at low pressure (suchas less than about 10 torr). However, this is illustrative only and inother embodiments, the ion-induced, UV-induced, or electron-inducedsequential CVD process of the present invention can be practiced in aprocess chamber operated at a pressure ranging from atmospheric pressureto low pressure. The present invention is defined by the appendedclaims.

We claim:
 1. A process for depositing a thin film on a substrate,comprising: (a) placing said substrate in a process chamber; (b)evacuating said process chamber; (c) introducing a flow of a firstreactant gas in vapor phase into said process chamber, said firstreactant gas forming an adsorbed saturated layer of said first reactantgas on said substrate; (d) evacuating said process chamber; (e) exposingsaid substrate to a flux of ions for inducing a chemical reaction ofsaid adsorbed saturated layer of said first reactant gas to form saidthin film; and (f) evacuating said process chamber.
 2. The process ofclaim 1, further comprising repeating said acts (c) through (f) to formmultiple layers of said thin film.
 3. The process of claim 1, furthercomprising: (g) introducing a flow of a second reactant gas in vaporphase into said process chamber before said act (e).
 4. The process ofclaim 3, wherein said exposing said substrate to said flux of ionsinduces a chemical reaction of said adsorbed saturated layer of saidfirst reactant gas and said second reactant gas for forming a compoundthin film.
 5. The process of claim 3, further comprising repeating saidacts (c) through (f) to form multiple layers of said thin film.
 6. Theprocess of claim 3, further comprising: evacuating said process chamberbetween said acts (g) and (e).
 7. The process of claim 1, furthercomprising after said act (f): (g) introducing a flow of a secondreactant gas in vapor phase into said process chamber; (h) exposing saidsubstrate to a flux of ions for inducing a chemical reaction of saidadsorbed saturated layer of said first reactant gas and said secondreactant gas to form a compound thin film; and (i) evacuating saidprocess chamber.
 8. The process of claim 7, further comprising repeatingsaid acts from (c) through (i) to form multiple layers of said thinfilm.
 9. The process of claim 7, further comprising: evacuating saidprocess chamber between said act (g) and (h).
 10. The process of claim1, wherein said flux of ions comprises inert gas ions.
 11. The processof claim 10, wherein said inert gas ions comprises argon ions.
 12. Theprocess of claim 1, wherein said flux of ions comprises reactive gasions.
 13. The process of claim 12, wherein said reactive gas ionscomprises one, or more, of nitrogen, oxygen, or hydrogen ions.
 14. Theprocess of claim 1, wherein said flux of ions is generated by impactionization.
 15. The process of claim 1, wherein said flux of ions isgenerated using a plasma discharge.
 16. The process of claim 1, whereinsaid flux of ions is generated in said process chamber.
 17. The processof claim 1, wherein said flux of ions is generated spaced apart fromsaid process chamber.
 18. The process of claim 1, wherein said flux ofions is generated in close proximity to said substrate.
 19. The processof claim 1, wherein said flux of ions is generated spaced apart fromsaid substrate.
 20. The process of claim 1, further comprising: heatingsaid substrate to an elevated temperature after said act (a).
 21. Theprocess of claim 20, wherein said elevated temperature is between 50° C.to 400° C.
 22. The process of claim 1, wherein said process chamber is achemical vapor deposition reactor.
 23. The process of claim 1, whereinsaid process chamber is operated at a pressure lower than about 10 torr.